Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The curved lines on a psychrometric chart indicates

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

2. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

3. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

4. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

None of these

Negative

5. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.376

0.4

6. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

7. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Involves no change in volume

Takes place at constant entropy

Takes place at constant temperature

8. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

9. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

10. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Sub-cooling or under-cooling

Super-cooling

None of these

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11. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Carnot

Reversed Carnot

12. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

13. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

14. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Water coolers

Domestic refrigerators

15. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

20°C

10°C

16. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

2.33

3.33

4.33

17. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

18. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

19. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-75.2°C

-77.7°C

20. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Equal to unity

Always more than unity

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21. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

22. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Good electrical conductor

Large latent heat

High risibility with oil

23. For obtaining high COP, the pressure range of compressor should be

Any value

Low

High

Optimum

24. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

25. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

5 tons

0.1 ton

26. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

27. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

28. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Miniature sealed unit

Centrifugal

29. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

30. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Ammonia

Brine

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31. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

32. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

33. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Wet bulb temperature of air

Ambient air temperature

34. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

35. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

36. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

37. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Inflammable

Non-inflammable and toxic

38. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

15 bar

30 bar

39. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

40. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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